Dengue- The Breakbone Fever

Dengue fever claims 29  lives in Tamilnadu. Chief minister to take measures to control the disease on war footing. Southern districts affected most. people advised to take precautionary measures, not to store water etc., 

All about Dengue:

Defn:

• Infectious tropical disease.
• Causative agent - Viral Disease, caused by a RNA virus.
• Transmitter - Aedes Mosquito.
• Target Victim - Humans(sometimes animals).

Cycle:

     Infected Person ------------->Mosquito------------>Healthy Human

Virus:

• Caused by the Dengue Virus, having four different serotypes: DEN1,DEN 2, DEN 3, DEN 4.
• Of these the asian varieties DEN 2, DEN 3 have high genetic variability and are associated with many secondary infections along with dengue. 

Mosquito:

• The mosquito is infected when it bytes an affected person, the virus first infects the gut and then spreads to the salivary gland.
• Incubation period around 8-12 days after which the mosquito spreads the disease to humans through  bite, usually done by female Aedes mosquito.
• Species causing infection: Aedes albopictus, Aedes polynesiensis, Aedes scutellaris complex.

Humans:

• After infection, circulates in blood for 2-7 days when fever develops.
• Infection in humans has three phases:
• Febrile phase: fever, rashes occur at this stage.
• Critical phase: Fluid accumulation in chest and abdomen, Hemorrhage in gastro intestinal tract.
• Recovery phase: Resorption of leaked blood in to the stream, sometimes reduced conciousness, seizures may occur.
• Infection by one serotype provides lifelong immunity to that serotype, but reduced immunity to other species.

Symptoms:

• Common Flu-like symptoms.
• High fever 40 C/ 104 F .
• Headache
• Pain behind Eyes.
• Nausea, Vomiting, 
• Swollen glands, Muscle and Joint Pain
• Rashes.

Severe cases:

• Plasma leaking
• Fluid accumulation
• Respiratory Distress.
• Severe bleeding.
• Organ Impairment.

Treatment:

• No specific vaccine available.
• Prevention only way:
• For vector(mosquito control) - Integrated Vector Management, avoid water collection, contamination etc.
• fever control drugs like paracetemol can be used
• Aspirin, Ibuprofen not advisable may increase bleeding.

Basics:

What is Serotype:

• Serotypes are distinctions within species of bacteria, virus, immune cells.
• Human immune cells are differentiating between self and foreign cells only based on this serotype matching.
• These are associated with the surface antigens.
• These cells play a vital role in organ transplants. When serotype match does not occur between donors and receivers, organ rejection occurs when the incoming organ is considered alien and is attacked by receiver's immune cells.

What are RNA viruses:

              These are viruses that have Ribonucleic acid as their genetic materials. As RNA polymerases lack proof reading ability of DNA polymerases, it is difficult to design Vaccines for these viruses. Also they have high mutation rates, and show high genetic variability adapting to drugs quickly.

                 Retro viruses are also having high mutation rates similar to RNA viruses and have RNA as their genetic materials but show DNA genetic materials once in to hosts. They convert their RNA in to DNA using an enzyme called Reverse Transcriptase. Then integrate this DNA to host Genome using integrase enzyme, to replicate as a part of host genome.